U.S. patent number 5,612,806 [Application Number 08/258,148] was granted by the patent office on 1997-03-18 for acknowledgement using subcarrier multiplexed tones.
This patent grant is currently assigned to GTE Laboratories Incorporated. Invention is credited to Robert Olshansky, Shing-Fong Su.
United States Patent |
5,612,806 |
Su , et al. |
March 18, 1997 |
Acknowledgement using subcarrier multiplexed tones
Abstract
Subcarrier multiplexed acknowledgment tones are used for
contention recovery in multiple-access WDM networks with basedband
data packets and subcarrier multiplexed control headers. Upon
receiving a data message from another node, the receiving node
sends a subcarrier acknowledgement tone to the transmitter thus
informing the transmitting node that the message has been received.
The thoughput of the network is significantly improved. In an
alternative embodiment, an acknowledgement is sent from the
receiver by impressing a data message on a subcarrier.
Inventors: |
Su; Shing-Fong (Southboro,
MA), Olshansky; Robert (Wayland, MA) |
Assignee: |
GTE Laboratories Incorporated
(Waltham, MA)
|
Family
ID: |
22280147 |
Appl.
No.: |
08/258,148 |
Filed: |
June 10, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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100513 |
Jul 30, 1993 |
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Current U.S.
Class: |
398/76; 398/1;
398/166; 398/89 |
Current CPC
Class: |
H04J
14/0298 (20130101) |
Current International
Class: |
H04J
14/02 (20060101); H04J 014/02 () |
Field of
Search: |
;370/121,71,124,76,95.1
;359/124,125,133,165,136 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pascal; Leslie
Attorney, Agent or Firm: Suchyta; Leonard C.
Parent Case Text
RELATED APPLICATIONS
The present invention is a continuation-in-part of U.S. Ser. No.
08/100,513, filed Jul. 30, 1993, now abandoned, having a
co-inventor with an obligation to assign to the same assignee as
this application. U.S. Ser. No. 08,/100,513, is entitled
"Wavelength Division Multiplexed Broadband Network with Subcarrier
Multiplexed Control Channel" and is incorporated by reference
herein.
Claims
What is claimed is:
1. An opto-electronic system, having a plurality of nodes N.sub.i
where i=1, . . . ,n, for sending message from one node N.sub.i to
another node N.sub.j where j=1, . . . ,n j not equal to i
comprising:
a transmitter means residing in said node N.sub.i for transmitting
a control channel signal to node N.sub.j which is centered at
frequency f.sub.j ;
a baseband transmitter means for transmitting a message from node
N.sub.i to node N.sub.j using an optical signal at wavelength
.lambda..sub.i ;
an acknowledgement means residing at node N.sub.j for notifying
node N.sub.i that said message is received;
whereby said acknowledgement means is a subcarrier multiplexed tone
unique to node N.sub.i.
2. An opto-electronic system, having a plurality of nodes N.sub.i
where i=1, . . . ,n, for sending message from one node N.sub.i to
another node N.sub.j where j=1, . . . ,n j not equal to i
comprising:
a transmitter means residing in said node N.sub.i for transmitting
a control channel signal to node N.sub.j which is centered at
frequency f.sub.j ;
a baseband transmitter means for transmitting a message from node
N.sub.i to node N.sub.j using an optical signal at wavelength
.lambda..sub.i ;
an acknowledgement means residing at node N.sub.j for notifying
node N.sub.i that said message is received;
whereby said acknowledgement means is a data message impressed on a
subcarrier multiplexed tone unique to node N.sub.i.
Description
FIELD OF THE INVENTION
The present invention relates generally to optical wavelength
division multiplexed communications networks and more specifically
to optical wavelength division multiplexecd communications networks
using a subcarrier multiplexed tone for acknowledgement.
BACKGROUND OF THE INVENTION
In any multiple-access WDM network using wavelength-tunable
receivers, a control channel is required to provide the receiving
node with information as to which wavelengths carry the incoming
messages. One approach for accomplishing this function uses a
common signalling wavelength shared by all nodes. However, this
approach requires a second DFB laser to transmit the control
headers, substantially increasing the cost of the opto-electronics
per node. Moreover, as the number of nodes increases, the density
of the control channels grows proportionally creating severe
contention for the control channels. Additionally, the data rate of
the control channels must increase as the density of the traffic
increases, forcing the control channel to transmit in the
gigabits/second range. One technique to avoiding these difficulties
is the use of subcarrier multiplexed (SCM) headers as the control
channels S. F. Su and R. Olshansky, "Performance of WDMA networks
with baseband data packets and SCM control channels," Proceedings
ECOC '92, pp. 585-588, September 1992. This approach eliminates the
need for a second DFB laser at each mode. It also alleviates the
control channel contention problem by channelizing the control
headers. As such, the control channel data rate is kept low,
typically in the 10-100 Mb/s range, making it possible to process
the control information with low cost silicon technology. To
maximize network throughput, it is desireous for the receiving node
to acknowledge and to confirm a successful transmission by the
transmitting node. A common wavelength or control channels on
subcarriers can be used for acknowledgment. The former approach
increases cost per node and the latter increases possible
contention between control channels and acknowledgments.
OBJECTS OF THE INVENTION
Accordingly, it is a primary object of this invention to obviate
the above noted and other disadvantages of the prior art.
It is a further object of the invention to provide for an
opto-electronic communications network allowing for increased
contention recovery.
It is a yet further object of the invention to provide for an
opto-electronic communications network allowing for increased
contention recovery by providing that the receiver of a data
message sent an acknowledgement to the sender as a subcarrier
multiplexed tone.
It is a yet further object of the invention to provide for an
opto-electronic communications network allowing for increased
contention recovery by providing that the receiver of a data
message sent an acknowledgement to the sender as a data message on
a subcarrier unique to the sender.
SUMMARY OF THE INVENTION
In one aspect of the invention the throughput of multiple-access
WDM network is improved by using subcarrier multiplexed
acknowledgment tones for contention recovery. Acknowledgement tones
are pure subcarriers carrying no data. Without contention recovery,
the theoretical maximum average throughput per node is limited to
0.5 as shown by C. S. Li, M. S. Chen, and F. K. Tong, "Architecture
and protocols of a passive optical packet-switched
metropolitan/wide area network using WDMA," IBM Research Report RC
17857, March 1992. Using subcarrier acknowledgment tones for
contention recovery, the data offered load per node can be
effectively greater than 1, and the maximum average throughput per
node is no longer limited to 0.5. Further, the frequency band of
the acknowledgment tones is separate from that of the control
channel subcarriers, thus eliminating concerns regarding contention
between control channels.
In another aspect of the invention, acknowledgement from a receiver
node are provided by impressing a short data response on an
assigned subcarrier to the transmitting node.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1. depicts a multiple-access WDM network with M nodes.
FIG. 2. depicts a frequency plan for SCM control headers and
acknowledgment tones according to the instant invention.
FIG. 3. shows throughput per node versus data offered load of a
network with 100 access nodes and 10 subcarriers for various data
packet lengths when employing the instant invention in a
multiple-access WDM network.
DETAILED DESCRIPTION OF THE INVENTION
A multiple-access WDM network with arbitrary topology is shown in
FIG. 1 with M access nodes. Each node comprises a fixed-wavelength
optical transmitter and one tunable optical receiver. The
transmitter at each node transmits messages on a separate
wavelength .lambda..sub.i (i=1.2, . . . , M) which is uniquely
allocated to that node. The tunable optical receiver can receive
any one of the M wavelengths. Each node is capable of transmitting
messages at its designated wavelength and simultaneously receiving
messages at any wavelength.
To transport a message, the transmitting node must inform its
intended receiving node to tune to the right wavelength. In
addition, the receiving node must send an acknowledgment back to
the transmitting node to confirm a successful reception.
Subcarriers are used to achieve these functions without adding a
separate wavelength. The control headers are transmitted using Q
subcarriers with frequencies f.sub.i, i=1,2 . . . Q and transmit
the acknowledgments using M subcarrier tones with frequencies
.nu..sub.i, i=1,2, . . . ,M, where Q<M. While each node may
transmit any of the above subcarriers, it may only accept two
unique subcarriers, the one assigned for the control header and the
one assigned for acknowledgment. Node j only accepts control header
and acknowledgement tone subcarriers at frequencies f.sub.j and
.nu..sub.j respectfully. Control header subcarriers are modulated
subcarriers carrying control header information. Acknowledgement
tone s are pure subcarriers carrying no data. A control header
subcarrier may be shared by up to q receiving nodes with
1<q<M, a separate subcarrier acknowledgment tone i s assigned
to each individual node.
Since the data rate associated with a control header is
approximately 10-100 Mb/s, silicon VLSI transceiver chips used for
Fiber Data Distribution Interface (FDDI) transmission are
commercially available and can provide the needed functionality.
FDDI uses 4B/5B encoding, operates at 125 Mbaud, and has a maximum
data transfer rate of 100 Mb/s. Using QPSK or differential QPSK
coding, a bandwidth efficiency of at least 1 bit/sec/Hz can be
achieved. Thus eight 125 Mbaud control channels could be placed in
each GHz of available bandwidth. With a baseband data rate of 2.5
Gb/s, then 8 subcarriers could be placed in the 3.0-4.0 GHz band.
If more control channels are required, they may be placed at higher
frequencies. Each acknowledgment tone occupies a bandwidth of a few
kHz. For a network of 100 nodes, the frequency band for the
acknowledgment tones is a few MHz.
An exemplary representation of the frequency plan for the SCM
control headers and acknowledgment tones is shown in FIG. 2. As is
shown, the acknowledgment tones may be placed between the data and
the control header frequency bands. However, in an alternative
embodiment the SCM acknowledgment tones may also be placed at any
frequency band, provided that they do not coincide with the data or
the SCM control headers.
The operation and protocol of the network is now described. A node
i desiring to transmit a message which consists of a control header
plus a data packet to node j, it will transmit the control header
on subcarrier f.sub.j using wavelength .lambda..sub.i, and
immediately begin transmitting the baseband data packet using the
same wavelength. At the same time its SCM receiver listens to
detect the acknowledgment tone at subcarrier frequency .nu..sub.i.
If the control header experiences no collision at node j, node i
will receive the acknowledgment tone .nu..sub.i from node j after a
round-trip propagation time. Node i completes transmission of the
data packet and then removes the message from its send queue.
However, if node i, after a round-trip propagation of the message
on the ring, does not receive an acknowledgment tone at wavelength
.nu..sub.i from node j, indicating that the control header has
experienced a collision, the sending node has the option of
immediately retransmitting the message or transmitting a new
message regardless of whether the earlier data packet is completely
transmitted or not. At node j, the SCM receiver will only accept
the electrical signals in the frequency bands of subcarrier f.sub.j
and .nu..sub.j. The control header processor following the SCM
receiver will read the incoming control header. It the incoming
control header experiences no collision, node j will send the
acknowledgment tone .nu..sub.i to node i. At the same time, it will
also instruct its receiver to receive the incoming wavelength
.lambda..sub.i. If the incoming control header experiences a
collision, node j will not send any acknowledgment tone to node i,
prompting node i to retransmit a message. Other nodes in the
network may carry out their operations simultaneously and
independently.
For a multiple-access WDM network without global synchronization
across the network, each node in the network is allowed to transmit
messages at will with no regard for other nodes. The throughput per
node can be derived as
where r is the normalized data packet length defined as the ratio
of data packet length to control header length in terms of time, G
is the aggregate average transmission attempts per time slot for
the entire network, M is the number of nodes, and Q is the number
of subcarriers for control headers. A time slot is defined here as
a control header length in terms of time. With the data offered
load to each node defined as G.sub.d =rG/M, (1) can be written
as
For connectionless transmission without acknowledgments, a message
from a node must be completely transmitted before the next message
can be transmitted from the same node. This means that the value of
G cannot be larger than M/r per time slot, and hence the maximum
data offered load G.sub.d is limited to 1. With G.sub.d =1 and r
very large, (2) has a maximum value of 0.5. In the acknowledgement
mechanism proposed here, an access node will immediately retransmit
a message (old or new) if it does not receive an acknowledgment
tone after a round-trip propagation time regardless of whether the
earlier data packet is completely transmitted or not. As such, the
value of G can be larger than M/r per time slot, and the value of
G.sub.d is no longer limited to 1. That is, the data offered load
could effectively be greater than 1. This will substantially
increase the throughput of the network. For illustration, (2) as a
function of the data offered load is plotted in FIG. 3 for a
network with 100 access nodes, 10 subcarriers for control headers,
and various data packet length. FIG. 3 clearly shows that for
longer data packets, the throughput is greater than 0.5 for G.sub.
>1.
While there has been shown and described what is at present
considered the preferred embodiment of the invention it will be
obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the
invention as defined by the appended claims.
* * * * *